1. Field of the Invention
The present invention relates to a gas chromatograph system of reduced size, weight and low power consumption for hand-held field applications. In particular, the present invention relates to a modular gas chromatography system which is capable of being interfaced with other portable analyzers.
2. Description of the Related Art
There has been a long-standing need for gas chromatography (GC) systems which are relatively small but have the capabilities and performance of full-size equipment. A desirable system would allow all of the individual components to be quickly attached and detached so as to allow interchange of components for different analyses. One early attempt at an improved GC system can be found, for example, in U.S. Pat. No. 3,403,545, the contents of which are incorporated herein by reference.
Over the years, several attempts have followed where size, weight, power consumption, heating/cooling, maintenance, speed and ease of use characteristics have been stressed. For example, in the commercial marketplace, there are a number of one or two-hand portable or larger GC systems. Each apparatus, however, has one or more undesirable features and/or cannot match the capabilities of most laboratory-sized systems that have a full range of state-of-the-art capabilities. Most commercially available field-portable GC devices are brief-case sized and hydrogen or helium is used as a carrier under isothermal GC conditions. One routine feature of full range systems is the ability to heat the GC in a systematic, controlled fashion while analyzing a sample. Hand-held GC systems, on the other hand, for example, lack temperature-programming capabilities for heating a sample. Thus, if the GC column had only a pre-set temperature and the compound of interest had a higher boiling point, then the compound would not elute from the column or it would creep along the column until it eventually eluted or decomposed. If a compound of interest has a higher boiling point than the GC column's pre-set temperature, the sample can be made to elute in a fairly straight-forward fashion by shortening the GC column, or increasing the flow rate of the gas through the column.
However, it is difficult and impractical to change the flow rate of the gas through the GC column in a linear fashion as is the case with temperature-programming. To elute various compounds with different boiling points at a pre-set GC column temperature, the flow rate of the gas through the GC column needs to be changed in an increasing fashion which means increasing the linear pressure difference across the GC column length. Increasing the pressure difference across the GC column in a linear fashion can be achieved in two ways: (1) increasing the pressure in the sampling end of the GC column or (2) decreasing the GC column length. The first approach is difficult and impractical for field-portable applications because the size of such apparatus would not fit within the palm of a hand. One pressure programmable assembly for GC columns requires a pressurized gas cylinder with a briefcase size pressure controlling unit. The second approach is completely impractical for portable GC's. In conclusion, it is undesirable to have a pressure-programmable GC column as well as a pre-set GC column temperature for field application purposes.
In view of the foregoing, improvements in hand-held GC systems have been desired. In addition to the lack of a temperature programming capability, it has been desired to provide GC systems which are smaller in size and have low power consumption needs.
The present invention addresses these needs.